Yup...it's a slow tranny, no use trying to hurry up the shifts. If you take your time shifting to second you should not have any problems. Unless it is cold, then my P5 will sometimes grind slightly/be notchy no matter what you do.
I also tried the redline tranny oil, but to be honest, I really didn't notice any difference. To me it seemed to get a little better when I racked up more miles, but it has not disappeared completely.
The downshift to 1st seems next to impossible if my car is moving. This to me took some getting used to, since my last car (1990 Dodge Colt) could down shift into 1st from about 35 mph without a complaint, if I asked it to. I didn't even have to rev match to help it in!